The official name and symbol of the Sox2 gene are “SRY (sex determining region Y)-box 2” and SOX2, respectively. The SOX2 gene provides instructions for making a protein that plays a critical role in the formation of many different tissues and organs during embryonic development. This protein regulates the activity of other genes by attaching (binding) to specific regions of DNA in order to turn other genes on or off. On the basis of this action, the SOX2 protein is referred to as a transcription factor. The SOX2 protein is especially important for the development of the eyes. At least 33 mutations in the SOX2 gene have been found to cause the SOX2 anophthalmia syndrome or the anophthalmia-esophageal-genital (AEG) syndrome. Some of these mutations prevent the gene from making any SOX2 protein, while others result in the production of an abnormally short, nonfunctional version of the protein. A few mutations change single protein building blocks (amino acids) in the SOX2 protein. All of these mutations disrupt the protein's ability to regulate genes essential for normal development of the eyes and other parts of the body. Abnormal development of these structures causes the signs and symptoms of SOX2 anophthalmia syndrome or anophthalmia-esophageal-genital (AEG) syndrome.
In lung development, Sox2 controls the branching morphogenesis of the bronchial tree and differentiation of the epithelium of airways. Over-expression causes an increase in neuroendocrine, gastric/intestinal, and basal cells. Under normal conditions, Sox2 is critical for maintaining self-renewal and the appropriate proportion of basal cells in adult tracheal epithelium. However, its over-expression gives rise to extensive epithelial hyperplasia and eventually carcinoma in both developing and adult mouse lungs.
In squamous cell carcinoma, gene amplifications frequently target the 3q26.3 region. The gene for Sox2 lies within this region, which effectively characterizes Sox2 as an oncogene. Sox2 is a key upregulated factor in lung squamous cell carcinoma, directing many genes involved in tumor progression. Its over-expression also activates cellular migration and anchorage-independent growth. The ectopic expression of SOX2 may be related to abnormal differentiation of colorectal cancer cells.
Lung cancer is the most frequent cause of cancer death in the United States. Squamous cell carcinoma of the lung is a major form of frequent and aggressive lung cancer. Recent studies show that the gene amplification of Sox2 that encodes a high mobility group domain-containing transcription factor is the most frequent and common event in squamous cell carcinomas of the lung, esophagus, and oral cavity at 3q22.33 (Bass, A. J., et al. (2009) Nat. Genet. 41, 1238-1242). Sox2 is a master regulator of pluripotent embryonic stem cells (ESCs) and adult neural stem cells. It can reprogram somatic cells into the induced pluripotent stem cells (iPSCs) with Oct4, Klf4, and Myc, or with Oct4, Lin 28, and Nanog. Sox2 also plays an essential role in the morphogenesis and homeostasis of the esophageal, tracheo-bronchial and bronchiolar epithelia. Sox2 acts as a lineage-survival oncogene for the expression of pluripotent stem cell signatures and for the lineage-specific gene expression of squamous cells in lung squamous cell carcinomas. Ectopic expression of Sox2 causes the oncogenic transformation of normal tracheobronchial epithelial cells. The Sox2 gene is also amplified in a fraction of small-cell lung carcinomas (Rudin et al. (2012) Nat. Genet. 44, 1111-1116). Sox2 is expressed in lung adenocarcinomas whose expression is associated with poor prognosis. Sox2 is frequently expressed in other types of poorly differentiated and aggressive human cancers. Sox2 is expressed in a subpopulation of stem cell-like ovarian cancer cells with other pluripotent stem cell proteins such as Oct4 or Lin28. In breast carcinomas, expression of Sox2 is associated with basal-like phenotypes and is required for mammosphere formation in culture, which is considered as part of stem cell-like properties.
Histone methylation is a major covalent modification of histones that provides the structural and functional characteristics of chromatin to epigenetically define gene expression patterns in a cell. LSD1 (lysine-specific demethylase 1), also known as KDM1, AOF2, or BHC110, is a highly conserved flavin adenine dinucleotide (FAD)-dependent lysine-specific demethylase that belongs to the monoamine oxidase family and specifically removes monomethyl- and dimethyl-groups from histone H3 at lysine 4 (H3K4), and in certain cells lysine-9 (H3K9). LSD1 is highly expressed in undifferentiated ESCs but progressively downregulated during differentiation. Loss of LSD1 in the mouse causes early embryonic lethality. Recent studies indicate that LSD1 is an essential epigenetic regulator of pluripotency in ESCs. It has been previously shown that the levels of LSD1 are elevated in pluripotent teratocarcinoma, embryonic carcinoma, and seminoma cells (Wang, J. et al. (2011) Cancer Research 71, 7238-7249).
Elevated levels of Sox2 in cancers also correlate with the presence of lymphnode and distant metastases colon cancers (Neumann, J., et al. (2011) BMC Cancer 11, 518). The over-expression and gene amplification of Sox2 were also found in a fraction of glioblastoma multiforme (GBM) (Alonso, M. M., et al. (2011) PLoS One 6, e26740) the most aggressive primary brain tumor. Lengerke et al. discloses that SOX2 expression was detected in 28% of invasive breast carcinoma as well as in 44% of ductal carcinoma in situ (DCIS) lesions (see Lengerke, C., et al. (2011) BMC Cancer 11:42). A score of SOX2 expression (score 0 to 3) was defined in order to distinguish SOX2 negative (score 0) from SOX2 positive samples (score 1-3) and among latter subgroup of SOX2 high expressors (score 3>50% positive cells). Overall, the incidence of SOX2 expression (score 1-3) was higher than previously reported in a cohort of lymph node negative patients (28% versus 16.7%). SOX2 expression was detected across different breast cancer subtypes and did not correlate with tumor grading. However, high SOX2 expression (score 3) was associated with larger tumor size (p=0.047) and positive lymph node status (0.018). Corresponding metastatic lymph nodes showed higher SOX2 expression and were significantly more often SOX2 positive than primary tumors (p=0.0432). It has further been shown that the embryonic stem cell factor SOX2 is expressed in a variety of early stage postmenopausal breast carcinomas and metastatic lymph nodes. These data suggest that SOX2 plays an early role in breast carcinogenesis and that high expression of SOX2 may promote metastatic potential. Further studies are needed to explore whether SOX2 can predict metastatic potential at an early tumor stage.
Histone acetylation is another post-transcription modification of histones controlled by two opposing enzymes: histone acetyltransferases (HATs) and histone deacetylases (HDACs) through adding and removing acetyl groups from lysine residues. In mammals, 18 HDACs have been identified, which catalyze deacetylation of histones and many other non-histone proteins. Histone deacetylase 1 (HDAC1) belongs to the Class I HDACs, which also include HDAC2, HDAC3, and HDAC8 and are mostly localized to the nucleus. HDAC1 and HDAC2 share substantial amino acid sequence homologies and are often found to co-exist in repressive transcriptional complexes. Both HDAC1 and HDAC2 can remove the acetyl group from the acetylated histone H3 at lysine 56 (H3K56) (Miller, K. M., et al. (2010) Nature Struct. Mol. Biol. 17, 1144-1151). However, HDAC1 and HDAC2 may have distinct functions because germ-line deletion of HDAC1 causes mouse embryo lethality before embryonic day 10.5 while HDAC2 specifically regulates synaptic plasticity and memory formation. HDAC1 is highly expressed in pancreatic ductal adenocarcinoma, colon cancer, ovarian cancer and lung cancer. A group of HDAC inhibitors are currently being tested in clinical applications. Most of these HDAC inhibitors, which usually belong to either aliphatic acids (i.e., butyrate and valproic acid), hydroxamates (i.e., tricostatin A and SAHA), benzamides (i.e., MS-275 and MGCD0103), cyclic peptides (i.e., FK228/resminostat), or electrophilic ketone hybrid molecules (i.e., trapoxin B or CHAP31) (Khan, O. and La Thangue, N. B. (2012) Immunology and Cell Biology 90, 85-94), interfere with the enzymatic activities of multiple members of class I HDACs or other HDACs. These HDAC inhibitors also usually induce histone H3 or H4 hyperacetylation, which correlate with broad cytotoxicities in different cancer cells.
Despite the knowledge that Sox2 is frequently over-expressed in variety of human cancers and acts as an oncogene to confer certain stem cell properties to carcinoma cells, compounds and compositions capable of selectively targeting Sox2-expressing cancer cells have remained elusive. Thus, there remains a need for selective inhibitors that target cancer cells that exhibit cancer stem cell properties and methods of making and using same.